java - PaintComponent() 可以在 AbstractAction 类中使用吗？

Question

我正在尝试编写一个程序来创建 JPanel，当用户按下 W、A、S 和 D 时，绘制的立方体将在窗口中导航(每次按下某个键时都会导航一定量) Pressed)，我创建了 MoveCubeUp 类，并重写了其中的 PaintComponent 方法，以便在调用该方法时重新绘制立方体，但它不起作用。有人能解释一下为什么吗？

public MyPanel(){
    …
    MoveSquareUp m=new MoveSquareUp(squareX, squareY);
    getInputMap().put(KeyStroke.getKeyStroke(("W"), "pressed"));
getActionMap().put("pressed", m)
}
class MoveSquareUp extends AbstractAction{
    public int squareXX, squareYY;
    public moveSquare(){
    squareXX=squareX+5;
    }
//I define the paintComponent method to draw the rectangle with its set height        
//at squareXX, squareYY
//action method is null (I am still trying to figure out binding keys to    
//actions but the paintComponent not working is preventing that
}

如果格式不正确，我深表歉意。第 1 篇文章:/Paint 方法是否需要在扩展 JFrame 的类中定义，如果是这样，我如何将它与 AbstractAction 类一起使用(或者如何完全避免使用 AbstractAction 类)？

Answer 1

问题的关键是您需要学会将模型与 View 和控制分开。这里的模型是你的 Sprite 的位置， View 是绘制这个位置的GUI，控件将保存包括你的AbstractAction在内的 Action ，如果可能的话，它们都应该彼此分开。

所以回答你的直接问题——任何paintComponent绝对不应该不位于AbstractAction内部，因为前者是 View 的关键部分，而后者是控件的关键部分。相反，让您的 View 反射(reflect)模型的状态，并且模型的状态将由控件(操作)更改。

关于您的其他问题，所有绘画方法都应该是 JFrame 的一部分吗:所有绘画方法都不应该位于扩展 JFrame 的类中，因为此类是一个复杂的类，它创建一个顶级窗口和几个子组件来显示您的GUI，如果您覆盖其绘制，则可能会以不良方式影响子组件的绘制。而是在扩展 JPanel 的类的 PaintComponent 方法中进行绘制，然后在 JFrame 中显示该对象。

例如:

package pkg3;

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.util.EnumMap;
import java.util.HashMap;
import java.util.Map;

public class GamePanel extends JPanel {
    private static final int ANIMATION_DELAY = 15;
    private final int HEIGHT = 400;
    private final int WIDTH = 600;
    private Square square;
    private EnumMap<Direction, Boolean> dirMap = new EnumMap<>(Direction.class);
    private Map<Integer, Direction> keyToDir = new HashMap<>();
    // !! private Circle circle;
    private Timer animationTimer;

    public GamePanel() {
        for (Direction dir : Direction.values()) {
            dirMap.put(dir, Boolean.FALSE);
        }
        keyToDir.put(KeyEvent.VK_UP, Direction.UP);
        keyToDir.put(KeyEvent.VK_DOWN, Direction.DOWN);
        keyToDir.put(KeyEvent.VK_LEFT, Direction.LEFT);
        keyToDir.put(KeyEvent.VK_RIGHT, Direction.RIGHT);
        setKeyBindings();
        setBackground(Color.white);
        setPreferredSize(new Dimension(WIDTH, HEIGHT));
        setFocusable(true);
        square = new Square();
        animationTimer = new Timer(ANIMATION_DELAY, new AnimationListener());
        animationTimer.start();
    }

    private void setKeyBindings() {
        int condition = WHEN_IN_FOCUSED_WINDOW;
        final InputMap inputMap = getInputMap(condition);
        final ActionMap actionMap = getActionMap();
        boolean[] keyPressed = { true, false };
        for (Integer keyCode : keyToDir.keySet()) {
            Direction dir = keyToDir.get(keyCode);
            for (boolean onKeyPress : keyPressed) {
                boolean onKeyRelease = !onKeyPress; // to make it clear how
                                                    // bindings work
                KeyStroke keyStroke = KeyStroke.getKeyStroke(keyCode, 0, onKeyRelease);
                Object key = keyStroke.toString();
                inputMap.put(keyStroke, key);
                actionMap.put(key, new KeyBindingsAction(dir, onKeyPress));
            }
        }
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        square.display(g);
    }

    private class AnimationListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent evt) {
            boolean repaint = false;
            for (Direction dir : Direction.values()) {
                if (dirMap.get(dir)) {
                    square.move(dir);
                    repaint = true;
                }
            }
            if (repaint) {
                repaint();
            }
        }
    }

    private class KeyBindingsAction extends AbstractAction {
        private Direction dir;
        boolean pressed;

        public KeyBindingsAction(Direction dir, boolean pressed) {
            this.dir = dir;
            this.pressed = pressed;
        }

        @Override
        public void actionPerformed(ActionEvent evt) {
            dirMap.put(dir, pressed);
        }
    }

    private static void createAndShowGUI() {
        GamePanel gamePanel = new GamePanel();
        JFrame frame = new JFrame("GamePanel");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(gamePanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        gamePanel.requestFocusInWindow();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

enum Direction {
    UP(0, -1), DOWN(0, 1), LEFT(-1, 0), RIGHT(1, 0);
    private int incrX;
    private int incrY;

    private Direction(int incrX, int incrY) {
        this.incrX = incrX;
        this.incrY = incrY;
    }

    public int getIncrX() {
        return incrX;
    }

    public int getIncrY() {
        return incrY;
    }
}

class Square {
    private int x = 0;
    private int y = 0;
    private int w = 20;
    private int h = w;
    private int step = 1;
    private Color color = Color.red;
    private Color fillColor = new Color(255, 150, 150);
    private Stroke stroke = new BasicStroke(3f, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND);

    public void display(Graphics g) {
        Graphics2D g2d = (Graphics2D) g.create();
        g2d.setColor(fillColor);
        g2d.fillRect(x, y, w, h);
        g2d.setStroke(stroke);
        g2d.setColor(color);
        g2d.drawRect(x, y, w, h);
        g2d.dispose();
    }

    public void setStep(int step) {
        this.step = step;
    }

    public void move(Direction dir) {
        x += step * dir.getIncrX();
        y += step * dir.getIncrY();
    }

}